1. Field of the Invention
The present invention relates to a voltage output circuit, a load drive circuit, and a method for outputting a voltage.
2. Description of the Related Art
Today, while motors are incorporated in a variety of electric products, such electric products consume a comparatively large amount of power as well as cause noise. Thus, various techniques are developed (see, e.g., Japanese Laid-Open Patent Publication No. 2009-177894).
A motor drive circuit is usually configured such that two transistors connected in series between a power supply and the ground are provided for a coil of each phase, and the coil is connected to a connection point of these two transistors. Then these transistors are on/off controlled in appropriate timing, thereby on/off controlling energization of each coil to rotate the motor.
At this time, in order to turn on the transistor on the upper arm side (power supply side) out of the two transistors connected in series, a voltage between a control terminal (e.g., gate terminal) and the connection point is required to be set higher than the predetermined threshold voltage. When the transistor on the upper arm side is turned on, however, the potential at the connection point increases up to close to a power supply voltage, and thus a voltage higher than the power supply voltage is required to be applied to the control terminal.
Therefore, it is necessary to generate a voltage higher than the power supply voltage using a voltage generating circuit such as a charge pump circuit, however, an oscillation signal such as a clock signal is required for the voltage generating circuit such as the charge pump circuit. Thus, the noise caused by this oscillation signal is generated. This noise is generated centering on a particular frequency according to the frequency of the oscillation signal, which can cause a significant effect on other surrounding electronic devices. This may occur similarly in the case where loads other than the motor are used.